This invention is directed to a method of making silicon oxide nanoparticles from silicon by utilizing a direct-current electric arc to generate the nanoparticles. The term silicon oxide is used herein to describe compounds with the empirical formula SiO.sub.x where x is less than or equal to two, as well as compounds described as silica.
Silicon-based luminescent species have spurred a great deal of scientific and technological study in the past five years. One such material is a weblike silica network consisting of nanometer-sized particles that photoluminesce in the blue region of the visible spectrum. This particular species and methods for its preparation are described in U.S. Pat. No. 5,580,655 (Dec. 3, 1996), jointly assigned to Virginia Commonwealth University, Richmond, Va., and Dow Corning Corporation, Midland, Mich.; hereafter referred to as the '655 patent.
Silica nanoparticles according to the '655 patent are prepared by laser ablation of silicon in an oxygen containing atmosphere. However, according to our invention, a simplified, improved process has been developed to produce luminescent nanoparticle silicon oxide. Our alternative process is cost-effective in terms of equipment and production through-put. Additional versatility is also gained with our invention by the ability to produce materials luminescing from blue to green to yellow-green. Transmission Electron Microscopy (TEM) of the luminescent SiO.sub.x powder shows that the main structure is an amorphous network of SiO.sub.x, but in some cases silicon nanoparticles less than about 5 nanometer in average particle diameter are present in the matrix as well. The photoluminescence is visible to the naked eye, and the material has the advantage of being environmentally stable and environmentally compatible.